Treatment of Small CHP Plant

and Short-term Use Diesel

Generators in the IAQM

Planning Guidance

Dr Ben Marner

Overview

• Small CHP can have significant impacts

Significant sources are being screened out in the

current guidance

• Diesel generators which aren’t used for long can

have significant impacts

But they are often ignored in assessments

Made using recycled slides

IAQM Screening Criteria

Comparison of Some NOx

Emission Sources

Google

‘Dispersion’ Criterion

Google

Earth

Micro CHP Case Study

2 x 5.5 kWe (20kW fuel input) CHP

25.5 m tall building

27 m high flue

Modelled using ADMS

CHPs add 0.7 µg/m3 annual NO2

‘Moderate’ Impact

Background NO2 is >40 µg/m3

Solution for CHP?

• Suggested “precautionary” criterion of 15kWe

• Alternatively tighten up ‘dispersion criterion’

But it would be very difficult to make this sufficiently

definitive

Short-term Use Diesel Generators

• Short-Term Operating Reserve

• Mobile Plant

e.g. construction sites

Temporary but used intensively

• Backup reserve / life safety

power cuts / fires

Regular routine tests – often 20

mins 1h each month

Diesel Generators

Diesel Generators

60 MW (fuel input)

(20 MWe) bank of

generators

60 km of M25

Generator Case Study

• Bank of 20 x 3MVA backup generators

12 hrs of testing per year (grew to 24 hrs)

IF testing coincided with worst-case met:

PC to 99.79th percentile of 1-h NOx = 4,086 mg/m3

PC to annual mean NOx = 13 mg/m3

Assessed the probability of significant impacts

Could not discount potential for significant impacts

Solution for Generators?

• Suggested Addition to Paragraph 6.20 J

“Description of construction phase impacts. These impacts will relate

primarily to dust emissions, which give rise to dust soiling and elevated

PM10 concentrations, although construction vehicles and plant and

vehicles may need assessment; particularly if diesel power

generators are to be used.”

• Suggested New Paragraph for Section 6

“When considering standby generators that are present

only in case of power failures or emergencies,

consideration should be given to any routine testing

procedures. Even operation for a few hours per year

can give rise to impacts that should be assessed”

Summary

• Please can we have more stringent criteria for

CHP?

• Please can we encourage robust assessments of

diesel generators?

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